Lien, a political novice and son of former Vice President Lien Chan (連戰), likened his campaign to the invasion of Normandy that led to the Allied victory in the European theater of World War II.

"The time has come for us to strike back. Today is our Normandy invasion, and we will move bravely forward for victory!" Lien declared in an attempt to boost voter morale ahead of what many consider Taiwan's mid-term elections.

Recent opinion polls show that Lien, a major figure in the KMT, has been trailing independent candidate Ko Wen-je (柯文哲), who expects to formally register later this week, by at least 10 percent.

As he was registering, supporters of social activist Wang Yi-kai, who is running for a seat on the Taipei City Council, shouted slogans "end plutocracy, let the people rule" — a shot at the extremely wealthy Lien clan.

Wang's supporters clashed with Lien's at one point but were immediately separated by police.

In Kaohsiung, Taiwan's second most populous municipality after New Taipei, incumbent Mayor Chen Chu did not show up in person to register.

But her opponent, the KMT's Yang Chiu-hsing (楊秋興) did. There, he talked up his achievements as magistrate of the now-defunct Kaohsiung County and pledged to boost the southern port city's economy if elected mayor.

Yang also took the opportunity to criticize the sitting mayor, saying Chen has saddled Kaohsiung with NT$240 billion (US$8.02 million) in debt and blasting her handling of the July 31 gas explosions that killed 31 people and injured over 300 in the city.

Chen Chi-yu (no relation), the DPP official who registered on Chen Chu's behalf, said the mayor and the city government will humbly face public criticism over the disaster and stressed that what the city needs now is "love, tolerance and unity" to overcome its wounds and get through hard times.

In Taichung, Taiwan's third most populous region, Mayor Jason Hu pledged he will work hard to get re-elected and let Taichung citizens come out as the "real winners."

Hu has been mayor in the central city since 2001, when it was still a provincial city before being upgraded to a special municipality in 2010.

Also on Tuesday, Huang Jing-tai (黃景泰), speaker of the city council in Keelung, registered his candidacy for the city of 373,000 people.

He announced that day that he has withdrawn his membership from the KMT to run in the northern city, following the ruling party's revoking his nomination amid allegations he took bribes from a real estate developer.